Inkjet printing techniques have been used in various fields of printing since images can be formed easily at low costs. One of the inkjet printing techniques is ultraviolet-curable inkjet printing wherein droplets of ultraviolet-curable ink are landed onto a recording medium and cured by irradiation with ultraviolet radiation to form thereon an image. Recently, ultraviolet-curable inkjet printing has been attracting attention for its ability to form images that exhibit high rub resistance and high adhesion even on recording media which lack ink absorption ability.
Further, studies have been made to realize high-speed printing for ultraviolet-curable inkjet printing, e.g., by using single-pass printing or high-speed serial printing with a small number of passes. High-speed printing, however, suffers from the drawback that the distance between adjacent ink droplets (dots) becomes small, so that adjacent dots are prone to be merged resulting in image quality reduction. In order to prevent merging of adjacent dots, studies have been made to increase the pinning property of ultraviolet-curable inkjet inks.
One of the methods that have been studied to increase the pinning property of ultraviolet-curable inkjet ink is to add a gelling agent so that the ink undergoes sol-gel phase transition depending on temperature. That is, it has been considered to prevent merging of dots by cooling the ink droplets for gelation as soon as they have been discharged in liquid state at high temperatures and landed on a recording medium. As the gelling agents to be added to the ink, stearone and the like have been disclosed (see, e.g., Patent Literatures 1 and 2).